A DPF is known as an effective technique for reducing PM discharged from a diesel engine.
A DPF is a PM collecting device that uses a filter, and both a soot component and an ash component discharged from the engine accumulate in the DPF. The soot component can be burned away by forcible regeneration, but the ash cannot be burned away by forcible regeneration and therefore accumulates gradually in the DPF. When the ash accumulates, the DPF becomes blocked, leading to an increase in exhaust gas pressure, and therefore an ash accumulation amount must be predicted periodically so that ash washing can be performed.
Ash is generated when engine oil enters a combustion chamber through a gap between a cylinder and a piston and is burned therein. It is therefore known that the ash accumulation amount correlates with an engine oil consumption amount.
Various techniques are available as ash accumulation amount estimating methods. For example, Japanese Patent Application Publication No. 2003-83036 (Patent Document 1) discloses a technique of determining the ash accumulation amount from a DPF differential pressure immediately after DPF regeneration is complete, Japanese Patent Publication No. 4032849 (Patent Document 2) discloses a technique of determining the ash accumulation amount by integrating a traveled distance, Japanese Patent Publication No. 3951618 (Patent Document 3) discloses a technique of determining an ash discharge amount from a map of an engine rotation speed and a fuel consumption amount and determining the accumulation amount by integrating the determined ash discharge amount, and Japanese Patent Application Publication No. 2006-29326 (Patent Document 4) discloses a technique of detecting an oil level using an oil sensor and calculating the ash accumulation amount by integrating the detected oil level.
Patent Document 1: Japanese Patent Application Publication No. 2003-83036
Patent Document 2: Japanese Patent Publication No. 4032849
Patent Document 3: Japanese Patent Publication No. 3951618
Patent Document 4: Japanese Patent Application Publication No. 2006-29326
However, with the technique of determining the ash accumulation amount from the DPF differential pressure immediately after DPF regeneration is complete, disclosed in Patent Document 1, the DPF differential pressure does not always increase in proportion to an increase in the ash accumulation amount, and in a condition where no soot has accumulated, the DPF differential pressure substantially does not increase relative to ash accumulation. It is therefore difficult to predict the ash accumulation amount alone from the DPF differential pressure with a high degree of precision.
Further, when soot accumulates in a DPF in which ash has accumulated, the DPF differential pressure is higher than in a case where ash has not accumulated, but since the amount of accumulated soot cannot be separated from the ash accumulation amount, it is difficult to estimate the ash accumulation amount quantitatively with a high degree of accuracy.
In the case of the technique of determining the ash accumulation amount by integrating the traveled distance, disclosed in Patent Document 2, the method is simple, but conditions such as an engine load cannot be taken into account, making it difficult to achieve estimation precision.
With the technique of determining the ash discharge amount from the map of the engine rotation speed and the fuel consumption amount and determining the accumulation amount by integrating the determined ash discharge amount, disclosed in Patent Document 3, a large number of test points, and accordingly a large amount of time, are required to create the map, and it is therefore difficult to secure precision over the entire map.
Further, with the technique of detecting the oil level using an oil sensor and calculating the ash accumulation amount by integrating the detected oil level, disclosed in Patent Document 4, the need to provide the oil sensor leads to an increase in cost.
Hence, various methods exist for estimating the ash accumulation amount, but at the same time, problems remain. It is therefore necessary to provide a simple method of estimating the ash accumulation amount precisely without an increase in cost.
Furthermore, ash, in contrast to soot, does not have carbon as a main component, and instead mainly contains components derived from metal-based additives contained in the engine oil. Therefore, the ash cannot be incinerated by combustion and must instead be washed, i.e. blown away by compressed air or the like. For this purpose, an operation must be performed in a dedicated service station having a washing facility.
Hence, a DPF regeneration support system that can issue an ash washing request to an operator accurately so that ash washing can be performed efficiently at a service station is also required.